1. Field of the Invention
The present invention relates to a novel method of manufacturing actuators, sensors and novel applications of the actuators and sensors manufactured according to the novel method.
2. Background Art
The creation of sensors and controllable actuators, or synthetic muscles, is known. Sensors and artificial muscles or actuators made from ion-exchange membranes are relatively new but also known.
U.S. Pat. No. 4,364,803, to Nidola et al., discloses a process for deposition of catalytic electrodes on ion-exchange membranes and an electrolytic cell made by the process. The process involves contacting a water-swollen, roughened membrane with an amphoteric organic or metal salt thereof, such as alkali metal salts thereof, e.g., platinum, palladium, and nickel. After further processing, the membrane is then contacted with a solution of the selected metal salt wherein sorption of the metal salts takes place mainly on the membrane surface in the vicinity of the polar groups of the polymer or the pre-adsorbed polar groups of the amphoteric organic. The absorbed/adsorbed metal creates the catalytic electrodes. The patent discloses operation of the electrode in the presence of sodium brine/caustic soda.
U.S. Pat. No. 4,522,698, to Maget, discloses a prime mover that uses pressure increases and decreases induced by converting molecules of electrochemically active material to ions, transporting ions through an electrolytic membrane and reconverting the ions to molecules. The prime mover includes gas-tight compartments filled with an electrochemically active material and separated by an electrolytic membrane, such as an ion-exchange membrane, that incorporates electrodes so that a voltage gradient can be established across the membrane to induce current flow through the membrane. When the current flows through the membrane, molecules travel through the membrane and are reconverted to molecules in the opposite compartment causing a pressure increase in the receiving compartment and a pressure decrease in the other compartment. The pressure changes are converted to mechanical motion that can be used as a driver for a mechanical load. The disadvantages of this technique are that the resulting motion is small and the pressure increase may rupture the membrane.
U.S. Pat. No. 4,748,737, to Charles et al., discloses a method of removing surface oxidation from particulates. The method includes removing oxide film from particulates with a liquid reducing agent or strong acid comprising an alkali metal., or a hydroxide of an alkali metal, wherein alkali metals such as sodium, lithium, potassium, or mixtures thereof are used.
U.S. Pat. No. 5,100,933, to Tanaka, et al., discloses the use of ionized cross-linked polyacrylamide gels as engines or artificial muscles; the gels can contain a metal ion and are capable of discontinuous volume changes induced by infinitesimal changes in environment. The gel is made by dissolving acrylamide monomers and bisacrylamide monomers in water, adding a polymerization initiator (in particular, ammonium persulfate and TEMED, or tetramethyl-ethylene-diamine) to the solution, soaking the gel sample in water to wash away all residual monomers and initiators, immersing the gel in a basic solution of TEMED for up to 60 days, then immersing the gel in a solvent (in particular, acetone, acetone in water, ethanol and water, or methanol and water). The primary disadvantages of these actuators are generally that the response time of the gel is much longer than that of other known actuator components and that the gel must be contained in the solvent bath. The gels are also mechanically brittle and easily broken.
U.S. Pat. No. 5,250,167, to Adolf, et al., discloses actuators or synthetic muscles, using polymeric gels contained in compliant containers with their solvents; these actuators undergo substantial expansion and contraction when subjected to changing environments. The actuators may be rigid or flexible and may be computer-controlled. The driver may also be electrolytic, where application of a voltage across the polymer gel causes a pH gradient to evolve between the electrodes. For example, filling the polymer fibers with platinum by alternatively treating them with solutions of platinic chloride and sodium borohydride obtains a reversible expansion and contraction of the fiber with the application of an electric field. The actuating gel itself is the only moving part required and the electric field may be only on the order of a few volts per centimeter. The disadvantage is that actuator performance is dictated by the parameters of the polymeric gel used. Furthermore, liquid containment is required to make the actuators stronger and not so easily broken.
U.S. Pat. No. 5,268,082, to Oguro et al., discloses an actuator element based on a membrane electrode that when subject to a DC voltage of 0.1 Volts to 2.0 Volts undergoes a displacement proportional to the square of its length (Col. 3; II. 4, 5). This description of the displacement in relation to membrane electrode length is patently erroneous. For example, for a length of unity, the displacement would be also unity. Consider further, for a length less than unity, the displacement would be greater than the length whereas for a length of 100, displacement would be less than the length, i.e., 10% of the length. Therefore, the specification relating to displacement is in error. Even if the specification were to have meant square xe2x80x9croot,xe2x80x9d ambiguity and vagueness would remain. Further ambiguities exist in the specification of this patent. For instance, in Example 4 (Col. 5; I. 27), a clamped membrane having a length of 5 mm extending beyond the clamp was placed in a salt water solution and exposed to a rectangular wave on the order of 0.1 Hz. For this example, a tip displacement of 10 mm was measured. This is a physical impossibility. In Example 5, an actuator element as used in Example 4 produced a displacement of +/xe2x88x920.36 mm (Col. 6; II. 18-20). The specification states that this displacement was about 1.8 times that of Example 4 (Col 6; II. 18-22), or approximately 18 mm. All of the foregoing descriptions related to membrane tip displacement are obviously in error. However, in another example, Example 3, a membrane 3 mm in length was placed in a 4% salt-water solution and exposed to 1.6 Volts resulting in a tip displacement of 0.3 mm, 10% of length. Therefore, one of ordinary skill in the art would conclude that the specification does not enable nor support tip displacements greater than 10% of the membrane length.
U.S. Pat. No. 5,389,222, to Shahinpoor, discloses electrically controllable polymeric gel actuators or synthetic muscles, using gels made of polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, or polyacrylamide contained in an electrolytic solvent bath. These actuators operate by reacting to changes in the ionization of a surrounding electrolyte by expanding or contracting, and can be spring-loaded and/or mechanically biased for specific applications. Polymeric gel configurations such as sheets, solid shapes or fiber aggregates are contemplated, as are the use of a salt water solution for the electrolyte, and a platinum catalyst in the actuator housing to recombine the hydrogen and oxygen produced as a result of electrolysis during ionization of the electrolyte. Again, liquid containment is required to maintain strength and electric controllability, and not enough deformation or displacement is generated.
U.S. Pat. No. 5,531,664, to Adachi et al., discloses a bending actuator having a coil sheath with a fixed distal end and a free proximal end. The distal end portion of the device is formed of an axially expanding and contracting shape memory alloy. The device produces adequate drive force to bend the bendable portions of medical probes incorporating the actuator. The ability to bend such probes facilitates in situ navigation.
xe2x80x9cDevelopment of a Novel Electrochemically Active Membrane and xe2x80x98Smartxe2x80x99 Material Based Vibration Sensor/Damper,xe2x80x9d by Sadeghipour et al., Smart Materials and Structures, Vol. 1, pp. 172-179, (1992), discloses xe2x80x9csmartxe2x80x9d materials developed from metalized NAFION(copyright) (E.I. du Pont de Nemours and Company) membranes that may be used for vibration sensing and damping applications. For sensing applications, the smart NAFION(copyright)-based viscoelastic material generates a voltage response when subject to mechanical vibrations. For damping applications, the material dissipates mechanical or pressure induced voltage potentials (electrical energy) as heat energy. The article also discloses a method of making the smart materials comprising steps of platinum deposition onto a NAFION(copyright) membrane and saturation of the platinum coated metal with hydrogen under high pressure, or alternatively, exposing the platinum coated membrane to dissolved hydrogen. Applications for the smart material include: integration into cantilever structures, such as robot arms, aircraft wings, etc., for damping; use as a vibration cell accelerometer; and use as a pressure cell. For vibration cell sensors, the authors reported voltage response over the frequency range of approximately 100 Hz to approximately 3000 Hz. Load response was also reported at 500 Hz and 1000 Hz. A plot of simulated tip deflection versus time for an electrically damped metal-NAFION(copyright) composite beam were reported for initial positive tip deflections of 1% of beam length. Because no beam lengths were given, the magnitude of displacement cannot be determined. All smart materials disclosed in this article rely on hydrogen as a cation.
Thus, there is an existing need for soft sensors and actuators that allow for a high degree of bending, i.e., displacement. Further, a need exists for such sensors and actuators to perform sensing and activation noiselessly and efficiently (as do biological muscles). Actuators with a low ratio of mass to power or a high ratio of power or force to mass are also in need, as are sensors with a high output signal strength in relation to sensory input.
In view of the above-described needs, it is a primary object of this invention to provide actuators and sensors for actuating and/or sensing displacement, rotation, force, torque, acceleration, frequency, concentration, charge, and degradation. In particular, a primary object of this invention is to provide actuators, sensors and actuators/sensors that are capable of undergoing unprecedented displacement.
In a preferred embodiment, the present invention comprises a sensing device comprising an ion exchange, lithium-treated membrane and a metallic coating on the membrane forming at least one electrode wherein bending of the membrane generates electrical potential between at least one electrode and another point. Lithium treatment during making of membrane-based sensors and/or actuators enhances overall sensitivity of sensors and activity of actuators in comparison to, for instance, sodium treatment. Lithium treatment includes, but is not limited to, use of LiOH, LiBH4, and mixtures of lithium and other cations. Sensing devices according to this embodiment comprise at least one electrode wherein incorporation of many electrodes is possible. However, the device is not limited to electrodes solely on the membrane because a point removed from the device can serve as an electrode, including a point within an electrically conductive solution.
In another preferred embodiment, the present invention comprises a sensing device comprising an ion exchange membrane having a length defining a relative path wherein the membrane comprises at least two parts fixed to positions along the path and a metallic coating on the membrane. The metallic coating forms at least one electrode wherein bending of the membrane displaces at least one part of the membrane, at a position between at least two fixed positions, thereby generating an electrical potential between the at least one electrode and another point. Sensor devices according to this embodiment serve to sense phenomena not only at end points of the sensor device but also at a point interior to the end points. For instance, such embodiments can sense wave phenomena that cause local or global displacement of the membrane-based sensing device. For this particular embodiment, the relative path need not be defined along a major length because membrane-based sensors of the present invention can take a variety of shapes, some having multiple lengths. The ability to sense along multiply defined lengths defining multiple paths is also a feature of the present invention. To accomplish sensing along multiple lengths, or even along a single length, the ability to incorporate multiple electrodes exists.
In yet another preferred embodiment, the present invention comprises a sensing device comprising an ion exchange membrane having a length defining a relative path wherein the membrane comprises at least one part fixed to a position along the path and a metallic coating on the membrane forming at least one electrode wherein bending of the membrane to displace at least one part of the membrane from the path by at least 1% of the length generates an electrical potential between the at least one electrode and another point. In this embodiment, the path defined by a length of the membrane-based sensor is relative because the sensor can move in space. For instance, for a sensor implanted in a body, movement of the body can alter the global position of the sensor, however, local displacement of the sensor with respect to the sensor itself generates a measurable signal. Another preferred embodiment of the present invention comprises a sensing device as described, however, bending of the membrane to displace at least one part of the membrane from the path by at least 0.1 mm generates an electrical potential between the at least one electrode and another point. Overall, some embodiments of the present invention rely on a scaler value displacement measured in length and some rely on a relative scaler value displacement measured in terms of percentage of a membrane sensor length.
Membrane-based sensors of the present invention comprise material properties. In a preferred embodiment of the present invention, an ion exchange membrane for use in a membrane-based sensor device has a material property selected from the group consisting of mechanical, rheological, chemical, thermal, magnetic, and electrical. Of course, such a device also has a metallic coating on the membrane wherein the metallic coating forms at least one electrode wherein application of an electrical potential between the at least one electrode and another point alters the material property.
A further preferred embodiment of the present invention comprises a sensing device comprising an ion exchange membrane and a metallic coating on the membrane wherein the metallic coating forms at least one electrode wherein displacement of the membrane generates a measurable signal useable in a feedback control system. In such a device the feedback control signal can feed back to the sensor device, for instance, to maintain the sensor in a predetermined position.
In another preferred embodiment, the present invention comprises a sensing and actuating device comprising an ion exchange membrane and a metallic coating on the membrane forming at least one electrode. Such a sensing and actuating device can comprise a feedback control system.
Several preferred embodiments of the present invention comprise a sensing or actuating device comprising an ion exchange membrane, a metallic coating on said membrane forming at least one electrode, and a surrounding coating forming an outer surface of the sensor or actuator device. The presence of a surrounding coating is advantageous for several reasons. For instance, the surrounding coating can encapsulate the membrane device. The surrounding coating can also provide for biocompatibility with biological material in which the sensing device is placed. Furthermore, a surrounding coating can effectively protect a pharmacological material that is in proximity with the sensing device. A surrounding coating of these embodiments of the present invention can permit transport of at least one member selected from the group consisting of mass transport and energy transport. In addition, a surrounding coating can comprise a non-porous material.
Combinations and variations of the aforementioned embodiments are useful and describe herewithin. For instance, a sensor/actuator membrane-based device with a permeable coating can function as a drug delivery system. By mechanical, electrical, and/or chemical means, the sensor can generate and transmit a signal to actuate a mechanism to induce drug delivery. Ideally for some applications, such a system is programmable to achieve zero order drug delivery, i.e., where the drug concentration within the body does not vary over time. When appropriately placed, devices according to the present invention, can stimulate natural processes within the body through a variety of means, including mechanical, electrical and chemical simulation.
The methods for making actuators, describe below, also applies for making sensor and sensor/actuators. The limitations associated with existing actuators and the methods for their manufacture are overcome by the present invention which provides a method of preparing actuators (synthetic muscles) comprising the steps of: rinsing an ion-exchange material; coating the ion-exchange material with a substance which undergoes chemical reduction in the presence of a reducing agent; and reducing the coating on the ion-exchange material by exposing the ion-exchange material to a reducing agent. In the preferred embodiment, the ion-exchange material comprises a material selected from the group consisting of ion-exchange membranes, ionomer membranes, ion-exchange resins, gels, beads, powders, filaments, and fibers, preferably an ion-exchange membrane, more preferably a polymer ion-exchange membrane, and most preferably a perfluorinated sulfonic acid ion-exchange polymer membrane. Rinsing is best performed in water. The ion-exchange material preferably has at least two surfaces and rinsing is preceded by roughening the surfaces of the ion-exchange material, such as by sandblasting with fine glass bead sandblast. Rinsing is also preferably preceded by cleaning the ion-exchange material in an ultrasonic water bath cleaner. The cleaning includes heating (preferably boiling) the ion-exchange material in solution (preferably acidic, most preferably HCl). Most preferably, the ion-exchange material has at least two surfaces and rinsing comprises (in order): roughening the surfaces of the ion-exchange material; cleaning the ion-exchange material; rinsing the ion-exchange material in water; and boiling the ion-exchange material in an aqueous solution (preferably acidic, such as an HCl solution). Rinsing preferably comprises at least two steps of rinsing and boiling the ion-exchange material in solution (in water, for a sufficient time to completely swell the ion-exchange material). Coating is preferably done with a metal, more preferably a noble metal, and most preferably with platinum, and is performed for a time sufficient to cover the ion-exchange material with a coating of approximately 3.75 mg/cm2 of the coating substance. Coating best comprises: immersing the ion-exchange material; and stirring. Immersing is preferably done into a solution containing a salt of a metal, such as a noble metal, palladium, or nickel, preferably a platinum salt, more preferably a platinum-amine complex, and most preferably Pt(NH3)4Cl2. The reducing step best comprises exposing the ion-exchange material to NaBH4. Reducing is preferably done in solution (e.g., aqueous) containing a reducing enhancer such as NH4OH, and involves continuously raising the temperature of the solution to a predetermined temperature. Reducing is best done at an elevated temperature in solution in a water bath at an elevated temperature and includes simultaneously stirring the solution in the water bath, and preferably simultaneously stirring the solution (at low speed) while adding the reducing agent. Most preferably, reducing comprises simultaneously: continuously raising the temperature of the solution to a predetermined temperature; and adding supplementary reducing agent at intervals. This preferably includes maintaining the temperature at the predetermined temperature and simultaneously adding a final amount of supplementary reducing agent when the predetermined temperature is reached, continuously stirring the solution after adding the final amount of supplementary reducing agent, rinsing the ion-exchange material (in water or HCl solution), and storing the ion-exchange material. Preferably, the reducing step comprises at least one reducing step comprising (in order): rinsing the ion-exchange material; immersing the ion-exchange material in a solution containing a reducing agent; rinsing the ion-exchange material; and storing the ion-exchange material. Preferably, the immersing is in a solution (aqueous) containing a salt of a metal such as a noble metal, palladium, or nickel, preferably a platinum salt, more preferably a platinum-amine complex, and most preferably Pt(NH3)4Cl2, as well as a reducing enhancer such as NH4OH, as well as a reducing agent such as H2NOH.HCl or H2NNH2.H2O. Reducing preferably comprises simultaneously: continuously raising the temperature of the solution to a predetermined temperature; and adding supplementary reducing agent at regular intervals for a time sufficient to substantially complete reduction, as well as testing the solution for completion of reduction such as by monitoring a color change produced by reduction. Rinsing preferably involves at least two rinsing steps, the first in water or an acidic (HCl) solution, or both in sequence, and is performed for a time sufficient to exchange cations in the ion-exchange material for H+ cations outside the ion-exchange material. The second is in water or a basic (NaOH) solution, or both in sequence, and is performed for a time sufficient to exchange cations in the ion-exchange material, such as H+ cations in the ion-exchange material are exchanged for alkali metal (Na+) cations outside the ion-exchange material. Preferably, a second of the at least one reducing and the rinsing are repeated, followed by a final rinsing step in water. After the two preferred rinsing steps, the ion-exchange material is preferably cleaned ultrasonically. Storing is preferably done in water.
The invention is also of a method of preparing an actuator comprising: at least one cleaning step; at least one step of rinsing an ion-exchange material; at least one step of coating the ion-exchange material with a substance which undergoes chemical reduction in the presence of a reducing agent; at least one step of reducing the coating on the ion-exchange material by exposing the ion-exchange material to a reducing agent; testing the solution for the completion of reduction; and at least one step of storing the treated ion-exchange material. In the preferred embodiment, the ion-exchange material is an ion-exchange membrane, an ionomer membrane, an ion-exchange resin, a gel, beads, a powder, filaments, or fibers, preferably an ion-exchange membrane, more preferably a polymer ion-exchange membrane, and most preferably a perfluorinated sulfonic acid ion-exchange polymer membrane. Rinsing is preferably done in water or solution (acidic, such as HCl, or basic, such as NaOH), and involves heating (boiling in solution) the ion-exchange material. At least two rinsings are best performed before coating. Coating is preferably done with a metal, preferably a noble metal, palladium, or nickel, and most preferably platinum. Preferably, at least one rinsing occurs before and after each reducing, and the reducing is done in the presence of a reducing enhancer (NH4OH). Exposing is best done to a reducing agent (NaBH4, H2NOH.HCl, or H2NNH2.H2O), preferably first to NaBH4, and later to H2NOH.HCl or H2NNH2.H2O. Preferably, reducing is done in solution and includes: heating the reducing solution; continuously stirring the ion-exchange material in the coating solution at low speed; and simultaneously raising the temperature of the solution while adding supplementary reducing agent. Testing preferably includes: mixing a test solution comprising a portion of the reducing solution; boiling the test solution; and detecting a color change in the testing solution during boiling. The portion is preferably about 2 ml and testing includes: adding NaBH4 to the test solution during boiling; and adding supplemental reducing agent to the reducing solution in which the ion-exchange material is immersed if a coloration is detected in the test solution during boiling, and terminating reducing otherwise. Storing is best done in water or in solution (acidic, such as HCl).
The invention is additionally of a method of preparing an actuator from an ion-exchange material comprising: roughening the ion-exchange material; a first step of cleaning the roughened ion-exchange material; a first step of rinsing the ion-exchange material; a first step of boiling the ion-exchange material; a second step of rinsing the ion-exchange material; a second step of boiling the ion-exchange material wherein boiling is performed for a sufficient time to completely swell the ion-exchange material; a step of coating the ion-exchange material with a substance comprising platinum; a third step of rinsing the ion-exchange material; a first step of reducing the coating on the ion-exchange material by immersing the coated ion-exchange material in a solution comprising a reducing agent whereby the coating undergoes chemical reduction in the presence of the solution comprising the reducing agent; simultaneously heating and stirring the ion-exchange material in the reducing agent; a fourth step of rinsing the ion-exchange material; a first step of storing the ion-exchange material; a fifth step of rinsing the ion-exchange material; a second step of reducing the coating on the ion-exchange material by immersing the coated ion-exchange material in a solution comprising a reducing agent whereby the coating undergoes chemical reduction in the presence of the solution comprising the reducing agent; simultaneously heating and stirring the ion-exchange material in the reducing agent; at least one step of sequentially rinsing the ion-exchange material; a second step of cleaning the ion-exchange material; and a second step of storing the ion-exchange material. The steps are preferably performed in the above order, and the last four repeated and including a final rinsing step prior to the second storing step.
The present invention is also of an actuator, produced by any of the above summary methods, comprising a treated ion-exchange material capable of a completely reversible deflection and means operably connected to the ion-exchange material for electrically driving the deflection of the ion-exchange material.
The invention is further of an actuator for use in a gripper mechanism comprising: at least two actuators, produced by any of the above methods, positioned opposite to each other and being capable of bending in equal and opposing directions; a power supply to the actuators to drive the mechanical bending of the actuators in opposing directions; electrical impulse conductors operably attached to the first end of each of the actuators for conducting electrical impulses across the actuators; and wiring, operably attached to the conductors and to the power supply, for electrically connecting the actuators to the power supply.
The invention is additionally of an actuator for providing three-dimensional movement, comprising: three actuators produced by any of the above methods, comprising a hollow triangular tube having a longitudinal axis wherein each of the actuators of the tube comprises a face of the tube; signal conductors, operably attached to the first end of each of the actuators, for conducting a signal across each of the faces of the tube, thereby stimulating each face of the tube at a phase angle apart from each adjacent face to produce a motion around the longitudinal axis of the tube; and a power supply for providing power to the signal conducting means; and a power conductor, attached to the signal conductors, for operably connecting the tube to the power supply. The signal is preferably a low amplitude alternating signal.
The present invention is still further of an actuator for use as a wing flap, comprising: at least two actuators, produced by any of the above methods, sandwiched in series in a stack configuration, each of the actuators formed in a planar layer and capable of acting as a series resistor element; power conductors, operably attached to the stack at the first end and the top and bottom surfaces, for conducting power across the stack; a power supply for supplying power to the stack; and connectors for connecting the power supplying means to the power conducting means. In the preferred embodiment, adhesive is placed between the actuators, preferably conductive and non-continuously applied.
The invention is also of an actuator for use as a robotic swimming structure, comprising: at least two actuators produced by any of the above methods, formed in an ion-exchange material having a first end, the ion-exchange material comprising a plurality of polymer gel fibers imprinted with means for conducting power through the ion-exchange material; conductors, operably attached to the ion-exchange material at the first end, for conducting an alternating low voltage across the ion-exchange material; a power supply for providing power to the conductors; a modulator for modulating speed of bending of the ion-exchange material varying the frequencies of the applied voltage; and a connector for operably connecting the conducting means to the power providing means. In the preferred embodiment, the actuator includes a buoyancy varier for varying the buoyancy of the swimming structure and a sealed housing, operably attached to the ion-exchange material at the first end, the housing comprising a signal generator (erasable programmable chip) and a power generator (a battery). The ion exchange material may be elastic or rigid.
The invention is yet further of an actuator for use as a resonant flying machine, comprising: at least one ion-exchange material actuator, prepared by any of the above methods, in the form of a planar layer having first and second ends, a top surface and a bottom surface; power conductors for conducting power across the ion-exchange material actuator, operably attached to the top and bottom surfaces of the ion-exchange material and along a central axis of the ion-exchange material equidistant from the first and second ends, whereby the ion-exchange material actuator is capable of reversibly bending in a flapping motion upon receiving power; a power supply for providing power to the conductors; and connectors for connecting the conductors to the power supply.
The invention is also of an actuator for use as a guide wire or a micro-catheter in intra-cavity medical applications, comprising: at least one ion-exchange material actuator prepared by any of the above methods, and formed in a small strip; a power supply for providing power to the strip; and connectors for connecting the strip to the power supply.
The invention is also of a sphincter-type or a squeeze-type actuator used in medical applications for incontinence and cardiac-assist devices.
Additional objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying Figures, and in part will become apparent to those skilled in the art upon examination of the following detailed description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.